The present invention relates to gas turbines, and, in particular, to a resilient seal for reducing air leakage and improving turbine engine efficiency.
In industrial gas turbines, shroud segments are fixed to turbine shell hooks in an annular array about the turbine rotor axis to form an annular shroud radially outwardly and adjacent to the tips of buckets forming part of the turbine rotor. The inner wall of the shroud defines part of the gas path. Conventionally, the shroud segments are comprised of inner and outer shrouds provided with complimentary hooks and grooves adjacent to their leading and trailing edges for joining the inner and outer shrouds to one another. The outer shroud is, in turn, secured to the turbine shell or casing hooks. Typically, each shroud segment has one outer shroud and two or three inner shrouds.
Two common designs have been used for configuring inner shrouds, i.e., an opposite hook design and a C-clip design. The opposite hook design is the more traditional approach and incorporates oppositely projecting hooks on the leading and trailing edges that are retained by the outer shroud.
The C-clip design is schematically illustrated in FIG. 1. As can be seen, like the traditional opposite hook design, the C-clip design also includes leading and trailing edge hooks 10, 12 projecting in opposite directions. However, in the C-clip design, the trailing edge hook 12 is retained with a separate C-clip 14, rather than being retained by the outer shroud 16, as in the opposite hook design.
Traditional inner shroud designs use a sealing scheme around the leading edge hook of the inner shroud. This scheme typically consists of an axial chording gap and a cloth seal segment gap for leakage control around the leading edge hooks. In the chording gap, there is a surface-to-surface gap between parts of the inner shroud and the outer shroud of the turbine. The chording gap is related to thermal chording which forms a gap between mating parts at an elevated temperature. The resulting equivalent gap is generally on the order of five to ten mils. Thus, the chording gap allows a significant amount of air to leak out from between the inner and outer shrouds into the hot gas path of the turbine, which reduces the operating efficiency of the turbine.
The cloth seal segment gap depends on the thermal growth or expansion of the inner shroud due to heating and manufacturing process capabilities. Here again, however, the cloth seal segment gap also allows air to leak out into the gas path of the turbine, again reducing the operating efficiency of the turbine.
A third inner shroud design, which is disclosed in U.S. patent application Ser. No. 10/348,010, filed Jan. 22, 2003, the contents of which are incorporated herein by reference, modifies the traditional stage one inner shroud to reverse the leading edge hooks, as compared to the traditional opposite hook design and the C-clip design. This reverse hook design also allows the use of a resilient seal on the leading edge hook of the inner shroud to improve turbine engine efficiency by reducing air leakage from between the inner and outer shrouds.